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United States Patent |
6,127,911
|
Haller
,   et al.
|
October 3, 2000
|
Transformer
Abstract
Transformer comprises a core (K1, K2), a primary winding (W1) and at least
one secondary winding (W2), which are arranged as conductors on one or
more layers of a flat carrier, and a coil former with a chamber system
having chambers (C1, C2), which accommodate the layers with the windings
(W1, W2). At least one of the chambers (C1, C2) is closed at least in
regions, with the result that long distances for creepage paths are
obtained. As a result of this, it is possible to adhere to existing safety
regulations for the mains power supply isolation even with very compact
dimensions and/or with full utilization of the width available for the
conductor tracks. The chamber system can be formed from two or three
plastic parts (P1, P2, P3) by mating. The layers with the conductor tracks
are routed laterally out of the chamber system in order to make contact
with terminals. In an advantageous refinement, webs with metallized slots
are arranged on walls of the chamber system, in order to make contact with
the conductor tracks (L). The slots are, for example, notched or
trough-shaped depressions in which the carrier layers latch into place and
are held thereby. The electrical contact afforded by the slots can be
additionally supported by a solder-paste application with subsequent
soldering. The lateral contacts mean that plated-through holes are avoided
in the case of the carrier layers, with the result that the latter can be
produced significantly more inexpensively. By virtue of the chamber
system, it is possible for the openings in a core, for example an E/E or
E/I core, to be utilized significantly better if the transformer has to
comply with a sufficient insulation strength, such as in the case of mains
power supply isolation, for example.
Inventors:
|
Haller; Hans-Otto (Niedereschach, DE);
Rilly; Gerard (Unterkirnach, DE);
Rodriguez-Duran; Jose-I (Villingen-Schwenningen, DE)
|
Assignee:
|
Deutsche Thomson-Brandt GmbH (Villingen-Schwenningen, DE)
|
Appl. No.:
|
243201 |
Filed:
|
February 2, 1999 |
Foreign Application Priority Data
| Feb 13, 1998[DE] | 198 05 914 |
| Jul 31, 1998[DE] | 198 34 615 |
Current U.S. Class: |
336/192; 336/198; 336/200; 336/232 |
Intern'l Class: |
H01F 027/29; H01F 027/30 |
Field of Search: |
336/298,208,192,200,232
29/602.1,602.23,602.24,602.25
|
References Cited
U.S. Patent Documents
4641114 | Feb., 1987 | Person | 336/200.
|
4837544 | Jun., 1989 | McDougal | 336/192.
|
5010314 | Apr., 1991 | Estrov | 336/198.
|
5291173 | Mar., 1994 | Yerman et al.
| |
5463365 | Oct., 1995 | Iwatani et al. | 336/192.
|
5598135 | Jan., 1997 | Maeda et al.
| |
Foreign Patent Documents |
001045 | Sep., 1996 | AT.
| |
0782154 | Dec., 1996 | EP.
| |
0782154 | Jul., 1997 | EP.
| |
2250394 | Jul., 1973 | DE.
| |
2233005 | Dec., 1977 | DE.
| |
8711808 | Nov., 1987 | DE.
| |
3722124 | Feb., 1988 | DE.
| |
3731286 | Mar., 1988 | DE.
| |
3700488 | Jul., 1988 | DE.
| |
4233086 | Apr., 1993 | DE.
| |
4337053 | May., 1994 | DE.
| |
19652039 | Jun., 1998 | DE.
| |
2250383 | Jun., 1992 | GB.
| |
Other References
Power Conversion Intelligent Motion, "1-MHz Resonant Converter Power
Transformer is Small, Efficient, Economical," Estrov. pp. 14-24, Aug.
1986, copy in 336-232.
|
Primary Examiner: Kozma; Thomas J.
Attorney, Agent or Firm: Tripoli; Joseph S., Laks; Joseph J., Sragow; Daniel E.
Claims
What is claimed is:
1. Transformer comprising:
a core,
a primary winding and at least one secondary winding which are arranged as
conductor tracks on flat carrier layers, and
a coil former with a chamber system accommodating said layers with the
windings and comprising at least two chambers in which said windings are
arranged, the primary and the secondary winding being arranged in
different chambers, characterized in that
webs with metallized slots are arranged in said coil former in order to
make contact with said conductor tracks,
said slots providing connections of conductor tracks being arranged at the
top side and underside of a double sided carrier layer, and
a slot encompasses an edge of a carrier layer, which is coated on both
sides, in a clamp-like manner for the purpose of contact-making between
said conductor tracks.
2. Transformer according to claim 1, characterized in that said slots are
distributed between at least two of said webs with said contact-making
being alternatively distributed, for a sufficient insulation spacing
between two of said slots.
3. Transformer according to claim 1, characterized in that said webs are
arranged on side walls of said coil former, and in that said carrier
layers are latched by in each case one of their edges in, in each case,
one of said slots.
4. Transformer according to claim 1, characterized in that said parts of
said coil former are composed of injection-moulded thermoplastic.
5. Transformer according to claim 4, characterized in that said webs are
produced by a two-shot MID process with selective metallization.
6. Transformer according to claim 1, characterized in that said carrier
layers are predominantly made of a plastic with an LCP structure, and in
that the same plastic is used for said coil former.
7. Transformer according to claim 2, characterized in that the parts of
said chamber system surround the openings in said core.
8. Transformer according to claim 7, characterized in that said coil former
comprises two parts, which are formed in such a way that three chambers,
one inner chamber and two neighbouring chambers, are produced by mating of
the parts, and that said inner chamber is closed in the region of said
core.
9. Transformer according to claim 7, characterized in that said coil former
comprises three parts, which are mated in such a way as to produce two
chambers closed in the region of said core, one for said primary winding
and one for at least one secondary winding.
Description
BACKGROUND
The invention is based on a transformer comprising a primary winding and at
least one secondary winding, which are arranged in the form of conductor
tracks on one or more layers of a flat carrier, in particular films or
printed circuit boards. Transformers of this type are used for example in
switched-mode power supplies having very high switching frequencies, in
particular frequencies of more than 50 kHz, thereby enabling the
transformer to be kept very small.
When the transformer is reduced in size, it is necessary to ensure
sufficient insulation between the primary side and the secondary side if
the transformer is not intended to be potted. This is particularly
important for switched-mode power supplies having mains power supply
isolation, for which safety regulations demand a creepage path for
electric surface currents from the secondary side to the primary side of
at least 6 mm, which must be adhered to throughout the entire transformer.
With given dimensions of the transformer core, the available useful volume
for the windings is thereby restricted. The safety regulations
consequently lead to larger components and higher power losses due to
increased non-reactive resistance and due to reduced magnetic coupling.
Known transformers of this type, illustrated in FIGS. 1a, 1b, contain for
example a core with two core parts K1, K2, primary and secondary windings
W1, W2 being arranged in the openings therein. The windings are arranged
as conductor tracks L on non-conductive layers F of a flat carrier, a
plurality of layers in each case lying one above the other, depending on
the number of turns required. A plurality of layers P are in this case
serially interconnected by plated-through holes T2 and have two external
terminals T1, T3. In order to achieve sufficiently long creepage paths
between the various windings, the outer and inner edges R of the layers P
must remain free, in other words are not permitted to have any conductor
tracks. The conductor tracks L are produced as copper tracks on the layers
P using etching technology, for example. Figures 1a, 1b are sectional
drawings corresponding to a central horizontal and a central vertical
plane of the transformer.
The object of the present invention is to specify a compact transformer of
the type mentioned in the introduction which has improved electrical
properties.
BRIEF SUMMARY OF THE INVENTION
The transformer of the invention comprises a coil former with a chamber
system having chambers which accommodate the layers with the windings. The
windings are arranged in at least two separate chambers, thereby producing
long distances for creepage currents between the windings without the
transformer having to be potted. In this case, the chamber system is
formed by at least two parts, which are formed in such a way that chambers
are produced by mating of these parts.
The chamber system can, for example, be formed by two parts, whose shape in
each case corresponds to an asymmetrical H in cross section and which are
mated in such a way as to produce one closed chamber in the region of a
core opening for the secondary winding and two adjacent, open chambers for
the primary winding. In a different exemplary embodiment, the chamber
system is formed by three parts, two parts being placed onto a central
part in such a way as to produce two closed chambers, one for in each case
one winding.
The parts of the chamber system may be produced for example from
injection-moulded thermoplastic, and their dimensions are chosen in such a
way that they latch together with one another in the course of mating at
the outer walls. In this case, the outer walls may lie one above the
otherlike a sandwich, thereby producing long distances for creepage
currents without necessitating any increase in the space required by the
chamber system.
The chamber system surrounds, in particular, the regions and the openings
of the core and is open on both sides, with the result that the layers
with the windings can be routed out on both sides in order to make contact
with terminals and for effecting contacts between different layers. In
addition, the outer part of the chamber system is provided with an
extension on its outer edge, with the result that the mated parts assume
the shape of an H in a section via the core, as a result of which the
creepage path is enlarged at these edges. The layers themselves may be
sufficiently enlarged at the open sides, as previously, with the result
that the safety regulations are likewise adhered to here. The
contact-making by the chamber system is not restricted as a result of
this.
Although the parts of the chamber system themselves take up part of the
space in the openings in the core, this is compensated for since the
conductor tracks now extend over the entire width of a layer up to the
walls of the chamber system. As a result of this, for example, the
utilizable copper area is increased by approximately 45% for a transformer
with a transformation power of approximately 140 watts. The electrical
power loss is reduced in the same ratio.
In addition, the chambers serve as an assembly aid and reduce the variation
in the geometry and, consequently, in the electrical properties on account
of assembly tolerances. Alternatively, the power of the transformer can be
increased as a result of this or the size of the transformer can be
reduced with a predetermined power. The layers are, for example, printed
circuit boards or films, for example Mylar or Kapton films.
If carrier layers which are coated on both sides are used, then
plated-through holes are necessary, which holes connect conductor tracks
arranged on the top side and underside of the carrier layer. In addition,
it is necessary to connect conductor tracks of a plurality of carrier
layers to one another, since only one or a few conductor tracks are
arranged on one side of a carrier layer and a predetermined number of
turns must be achieved for a transformer winding. However, this makes this
transformer considerably more expensive and makes automatic production
more difficult.
In order to make contact with the conductor tracks, the chamber system
therefore has, in an advantageous refinement, webs with metallized slots
which establish connections between conductor tracks which are arranged on
the top side and the underside of a carrier layer coated on both sides, or
between conductor tracks of two adjacent carrier layers. This makes it
possible, in particular, to avoid plated-through holes of carrier layers.
A slot in this case encompasses, like a clamp to a certain extent, the
edge of a carrier layer coated on both sides and thereby connects two
conductor tracks, in the case of which, for example, one end in each case
is led up to this edge.
The webs of the chamber system and the metallized slots can be produced by
the two-shot MID ("moulded interconnect devices") process together with
the chamber parts. The MID process, a plastic injection-moulding process,
makes it possible to produce filigree structures made of thermoplastics
together with metallic conductor tracks, which can replace conventional
printed circuit boards. The webs are in this case selectively metallized
for the production of the slots.
For a lower contact resistance, the metallized slots may additionally be
strengthened by electroplating. To afford assistance, it is possible to
provide a solder-paste application with a downstream soldering operation.
The contacts are distributed between two or more webs in order to ensure
an interspace having a sufficient insulation spacing between two slots. In
the case of the two-shot MID process, activation by means of palladium
nuclei can be used in the first shot, for example, the said activation
improving the adhesion of a subsequently applied copper layer.
For the carrier layers it is possible to use, in particular, an LCP (Liquid
Crystal Polymer) structure to which conductor tracks can be applied using
the Futuron process, for example. This makes it possible to produce
conductor track thicknesses with 35 .mu.m or 70 .mu.m of copper for higher
current loading, in other words conductor track thicknesses which cannot
be produced by the "hot stamping" process. The LCP film is highly
temperature-resistant, thereby enabling soldering processes, for example
the Reflow process, to be used for the chamber system with the carrier
layers arranged therein.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is explained in more detail below, by way of example, with
reference to schematic drawings, in which:
FIGS. 1a, 1b show a planar transformer according to the prior art,
FIGS. 2a, 2b show a transformer according to the invention with a chamber
system made of three parts and two chambers, and
FIGS. 3a, 3b show a transformer according to the invention with a chamber
system made of two parts and three chambers,
FIG. 4 shows instances of contact-making of conductor tracks by means of
trough-shaped slots.
FIG. 5a shows a chamber part with webs for contact-making,
FIG. 5b shows a lateral view of the chamber part of FIG. 5a in section, and
FIG. 6 shows a copper structure for electroplating slots on a chamber part.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The transformer illustrated in FIG. 2a contains a core having two core
parts K1, K2 in the form of an E/E core, the turns of a primary winding W1
and of at least one secondary winding W2 leading through the openings in
the said core. The windings W1, W2 are in this case arranged in a chamber
system composed of three parts P1, P2, P3 in such a way that two closed
chambers C1, C2 are produced in the region of the sectional plane, the
windings W1, W2 being arranged separately from one another in the said
chambers. One of the parts P2 has the shape of a double-T, referring to an
opening, and the other two parts P1, P3 have the shape of a U. The two
parts P1, P3 are produced to fit with the central part P2 and are mated
with the latter to produce the closed chambers C1, C2. In this case, the
U-shaped parts P1, P2 are seated within the T-shaped part P2. Long
creepage paths are produced between the two windings W1 and W2 on account
of the double-T of the part P2 arranged in the centre.
The windings W1, W2 are constructed from a plurality of wrappings of
carrier layers F, between which an insulating layer is arranged. In this
exemplary embodiment, the carrier layers F are provided with conductor
tracks on both sides. Carrier layers coated on one side can likewise be
used, however. An exemplary arrangement of a conductor track L on the
carrier layer F can be seen in FIG. 2b, where five turns are arranged on
one side with a contact T1 at the beginning and a contact T2 at the end of
the conductor track. The end of the conductor track T2 is routed via a
plated-through hole to the underside of the carrier layer F, on which
turns are likewise arranged, and is routed back to the top side again by
means of a plated-through hole T3.
FIG. 2b illustrates the transformer of FIG. 2a in a sectional plane
perpendicular to the sectional plane of FIG. 2a, the sectional plane
passing through the core part K1. The layers F and the chamber system with
the parts P1, P2 completely fill the openings in the core K1. In this
case, the chambers of the chamber system are completely closed in the
region of the openings in the core and in the core, and only at the two
sides on the left and right are the layers F with the conductors L routed
out from the chambers C1, C2 for the terminals of the windings W1, W2. The
terminals T1, T3 of one winding W1 are located, for example, on the
left-hand side and the terminals of the other winding W2 are then located
oppositely on the right-hand side, thereby ensuring a sufficient spacing
for mains power supply isolation. The double-T-shaped part P2 additionally
contains an extension P2L at its edges, for the purpose of enlarging the
creepage paths in this region. This arrangement makes it possible for the
conductor tracks L to extend over the entire width of the layer F in the
region of the core openings.
FIGS. 3a, 3b illustrate a transformer with a chamber system containing an
inner part P4 and an outer part P5, which form a closed chamber C4 and two
open chambers C3, C5. In the section of FIG. 3a, the two parts P4, P5 have
the shape of an asymmetrical H, with a slightly different size, so that
one can be placed into the other. This allows to arrange the secondary
winding W2 in the closed, central chamber C4 and the primary winding W1,
divided into two halves, in the two outer chambers C3, C5. The arrangement
of the primary winding W1 in the central chamber C4 and of the secondary
winding W2 in the two outer chambers C3, C5 is also possible. The shape of
the outer walls like an asymmetrical H means that long creepage paths
between the windings W1 and W2 are likewise obtained in this case.
FIG. 3b shows the transformer of FIG. 3a in a sectional plane corresponding
to that of FIG. 2b. In this case, the conductor tracks L of a layer F are
likewise extended completely over the width of the inner chamber of the
part P5. In this case, the chamber system having the parts P4 and P5 is
likewise closed only in the region in the core and around the openings
therein, and open on both sides for the contact-making of the terminals T1
and T3.
The thickness of the walls of the chamber parts P4 and P5 can be kept very
small, for example 0.4 mm. The carrier layers F may protrude from the
chamber system outside the openings in the core parts K1, K2, as described
above, for example in order to perform contact-making at the terminals T1
and T3. The required insulation spacing can be produced here, without any
disadvantages, by a sufficient edge R on the carrier layer F.
The transformer can be used for example in a switched-mode power supply, in
which the primary winding W1 is connected to a switching transistor and,
via a bridge rectifier, to the mains power supply. A plurality of
secondary windings for supplying loads can be arranged both on the
secondary side with mains power supply isolation and on the primary side
without mains power supply isolation. The mains power supply isolation
proceeds on the circuit board on which the transformer is arranged in a
device, underneath its core. The question of whether this secondary
winding is provided with mains power supply isolation or no mains power
supply isolation depends on whether the terminals of a secondary winding
are routed out towards the left or towards the right. The windings can be
distributed in a corresponding manner between the chambers of the chamber
system. However, other configurations, in particular with other core
shapes, are likewise possible.
In an advantageous refinement, in order to avoid plated-through holes, the
chamber system contains webs S with metallized slots N, illustrated in
FIG. 4, which establish connections between conductors L on the top side
and the underside of the carrier layers F. The webs S are arranged on
chamber walls PK, which rise vertically from the bottom part B of a
chamber part in this exemplary embodiment. The slots N may be designed
such that they are trough-shaped, as in this exemplary embodiment, or
notched, with the result that the carrier layers F latch into place with
an edge. In this case, a metallized slot N surrounds the edge like a clamp
and thereby establishes electrical contact between a conductor track L on
the top side and a conductor track L on the underside of the relevant
carrier layer F. The depth of the slot may have values in the region of
0.5 mm, for example.
The carrier layer that is used may be, in particular, an LCP structure
having a thickness of 0.05 mm, which can be provided with conductor tracks
having a thickness of 35 .mu.m or 70 .mu.m. In order to support the
contact-making between the conductor tracks L on the top side and
underside of the carrier layer F, it is also possible to use, in addition,
a solder-paste application LP, which is introduced into the slots N.
Appropriate heating, for example in a Reflow process, enables the solder
paste to fuse with the conductor tracks L and the metallization layer of
the slot N. A conductive adhesive may also be used instead of this
soldering process.
Insulating layers IS are arranged between the carrier layers F, in order to
avoid short circuits between conductor tracks. In particular, the web S
contain a metallized slot N only for every second carrier layer F, thereby
producing a sufficient insulation spacing between two slots.
FIG. 5a illustrates an inner chamber part P4 in a plan view, into which
chamber part the carrier layers F, for example the secondary winding W2,
are inserted in the form of a stack. The inner chamber part contains a
bottom part B, on which the bottommost carrier layer F bears in as planar
a manner as possible, and side walls PK, which determine the width of the
carrier layers. This chamber part P4 can be used for an E/E core, for
example, the central core limb of the core passing through the opening OE
in the chamber part P4.
The winding arranged in the chamber part P4 is completely enclosed, in the
region of the core and the openings therein, by a second chamber part, not
illustrated, thereby making it possible to use the entire width between
the chamber walls PK for conductor tracks on the carrier layers F. The
chamber part P4 and the associated, terminating outer chamber part are
similar to the chamber parts P4 and P5 of FIG. 3a, but have lateral
extensions. As a result of this, it is possible to arrange further webs in
the inner chamber part P4, the webs S1, S2 and S5, S6 in the exemplary
embodiment of FIG. 5a. The webs S3 and S4 can also be processed from the
side through a cutout AS.
The structure of the webs S3, S4 is revealed by FIG. 5b, which shows a view
of the chamber part P4 in the section A-B. Metallized slots N1-N5 have
been worked into these webs S3, S4, which slots in each case establish
contact between a conductor track on the top side and the underside of a
carrier layer. Since the slots N1-N5 are distributed between two webs, a
sufficient insulation space in between the slots is produced. As a result
of this, one web is used in each to effect contact with next-but-one
carrier layers, with the result that two webs are sufficient. For example,
upper and lower conductor tracks of five carrier layers make contact with
one another by means of the five slots N1-N5, in order to avoid
plated-through holes.
The webs S3, S4 only establish contacts of conductor tracks on the top side
and underside of carrier layers, in order to avoid plated-through holes.
Contacts between carrier layers can likewise be established by the
invention but, in this embodiment, are intended to be realized on the
outer edge of the carrier layers together with the terminals of the
winding.
FIG. 6 illustrates the slots N1-N5 of the webs S3, S4 in an enlarged manner
in a detail drawing. A copper structure KS, which is not present in FIG.
5b, can additionally be seen here. This copper structure effects
electrical connection to the slots N1-N5, by means of which the
metallization of the slots N1-N5 can be reinforced by electroplating in a
copper bath during production. The copper track KS is removed again after
the electroplating. The copper layer KS can be applied directly on the
wall PK.
By using the same LCP structure for the carrier layers F and the chamber
parts P4, P5 and/or for the parts P1-P3, it becomes possible for the
transformer to be completely recycled. Separation of plastic and metal
with a satisfactory degree of purity in the case of an LCP structure have
already been demonstrated. Material recycling would be important in
particular for television sets, since they contain a very large number of
plastic parts.
On account of the outstanding injection-moulding properties of the LCP
structures, it is possible to use wall thicknesses in the region of 0.4 mm
for the chamber parts, as a result of which the area loss in the openings
in the core is kept low with this wall thickness. The widening of the
utilizable area on the carrier layers in comparison with earlier
transformers enables the number of wrappings of carrier layers to be
reduced, with the result that the additional costs arising due to the
chamber system can be compensated for just by the saving of a winding
wrapping. In addition, the transformer has improved electrical properties
due to better utilization of the core openings.
The chamber system which has been explained with reference to FIGS. 2-6
relates essentially to an E/E core or E/I core. However, other
configurations, in particular for other core shapes, are likewise
possible. Transformers of this type may be used for example in resonant
converter switched-mode power supplies which provide relatively high power
outputs in the region of considerably more than 100 watts, for example for
plasma television sets or television sets having large picture tubes.
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